The Transantarctic Mountains peak out from the vast Antarctic ice sheet. An international team of scientists recently reported that Antarctica could be an overlooked but important source of methane, a potent greenhouse gas.

Gas leak?

A new study by an international team of scientists in the Aug. 30 issue of the prestigious journal Nature suggests that Antarctica could be an overlooked but important source of methane, a potent greenhouse gas.

The new study suggests that old organic matter in sedimentary basins located beneath Antarctica’s ice sheets may have been converted to methane by microorganisms living under oxygen-deprived conditions. The methane could be released to the atmosphere if the ice sheet shrinks and exposes these old sedimentary basins.

“It is easy to forget that before 35 million years ago, when the current period of Antarctic glaciations started, this continent was teeming with life," said study co-author Slawek Tulaczyk, a professor of Earth and planetary sciences at the University of California, Santa Cruz.

Photo Credit: J. L. Wadham

Frozen lake sediments can be seen in this view of the ice margin of an Antarctic glacier. When ice sheets form, they overrun organic matter such as that found in lakes, tundra and ocean sediments.

Photo Credit: G. Lis

Researchers extracted blocks of ice containing subglacial sediments from the margins of different glaciers and ice sheets for use in long-term incubation experiments to look at subglacial methane production.

“Some of the organic material produced by this life became trapped in sediments, which then were cut off from the rest of the world when the ice sheet grew,” explained Tulaczyk, whose work is supported by the National Science Foundation. “Our modeling shows that over millions of years, microbes may have turned this old organic carbon into methane.”

Tulaczyk is also a principal investigator on an upcoming project to access a subglacial lake and water system called WISSARD, for Whillans Ice Stream Subglacial Access Research Drilling. Fieldwork for the project, which involves using a hotwater drill to bore through the ice sheet to reach the subglacial environment, is scheduled to begin in 2012-13.

The researchers estimated that 50 percent of the West Antarctic Ice Sheet and 25 percent of the East Antarctic Ice Sheet overlies pre-glacial sedimentary basins containing about 21,000 billion metric tons of organic carbon.

“This is an immense amount of organic carbon, more than ten times the size of carbon stocks in northern permafrost regions,” said lead author Jemma Wadham at the University of BristolSchool of Geographical Sciences. “Our laboratory experiments tell us that these sub-ice environments are also biologically active, meaning that this organic carbon is probably being metabolized to carbon dioxide and methane gas by microbes.”

The researchers numerically simulated the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model. They found that subglacial conditions favor the accumulation of methane hydrate, which is methane trapped within a structure of water molecules, forming a solid similar to regular ice.

They also calculated that the potential amount of subglacial methane hydrate and free methane gas could be up to four billion metric tons, a similar order of magnitude to some estimates made for Arctic permafrost. The predicted shallow depth of these potential reserves also makes them more susceptible to climate forcing than other methane hydrate reserves on Earth.

Potential methane release during episodes of ice-sheet collapse could act as a positive feedback on global climate change during past and future ice-sheet retreat.

“Our study highlights the need for continued scientific exploration of remote sub-ice environments in Antarctica, because they may have far greater impact on Earth’s climate system than we have appreciated in the past,” Tulaczyk said.